1. Field of the Invention
The present invention relates to dispersing elements for dispersing incident light into different wavelength bands. In addition, the present invention relates to solid-state image pickup devices, and imaging devices such as digital cameras, employing the dispersing element.
2. Description of the Background Art
With the spread of digital cameras, solid-state image sensors such as CCD image sensors and CMOS image sensors have been widely used. A solid-state image sensor has a plurality of light receiving regions on a light receiving surface, and converts light incident on each region into an electric signal according to the intensity of the incident light, thereby generating image information.
In the digital camera market, reduction in device size or increase in definition of taken image are demanded. In order to reduce the size of an image sensor or increase the number of pixels in an image sensor, the area of the light receiving region corresponding to one pixel must be reduced. However, the smaller the area of a pixel is, the smaller the amount of light incident on the region of the pixel is, which causes reduction in sensitivity of the image sensor.
In the conventional solid-state image sensor, a color filter is provided in front of (on the incident side) of the light receiving region of each pixel in order to obtain a color image. The color filter absorbs or reflects light of a wavelength band other than a desired wavelength band, and thereby only light of a specific wavelength band is converged to each pixel of the solid-state image sensor. A specific configuration of the solid-state image pickup device will be described with reference to FIG. 13.
FIG. 13 is a schematic configuration diagram illustrating a part of the conventional solid-state image pickup device. Red, green, and blue color filters 210, 220, and 230 are provided corresponding to light receiving regions 300, 400, and 500 for performing photoelectric conversion, respectively. A microlens 100 is provided above each of the color filters 210, 220, and 230 so that incident light is converged to each light receiving region. For example, Japanese Laid-Open Patent Publication No. 2008-71920 discloses such a solid-state image pickup device using microlenses.
International Publication No. WO2005/069376 discloses a solid-state image pickup device in which a color filter having wavelength selectivity is formed by using an optical microlayer film, and the thickness of the color filter is reduced to achieve size reduction in the solid-state imagine pickup device. Japanese Laid-Open Patent Publication No. 2005-79674 discloses a 3-CCD imaging device in which incident light is dispersed using a photonic crystal, and the dispersed beams are converged to three solid-state image pickup devices for red, green, and blue, respectively.